1. Field of the Invention
The present invention relates to a display device and method of manufacturing the same. Particularly, the present invention relates to a display device provided with display panel, that has a plurality of organic electro luminescent element arranged as a display pixel.
2. Background of the Invention
Recently, as a new generation display device that follows liquid crystal display device (LCD), that is heavily used as monitor and display for personal computer, image apparatus, mobile information apparatus, and the like, research and development is made actively on display (display device) provided with display panel of luminescent element type, that have self luminescent element such as organic electro luminescent element (hereinafter abbreviated as “organic EL element”), luminescent diode (LED), and the like, in two dimensional arrangement.
In particular, concerning a luminescent element display panel of active matrix driving type, when compared to liquid crystal display device, display response speed is fast, and there is no dependency on viewing angle. In addition, high luminance and high contrast, as well as higher resolution of image quality and the like can be achieved. Further, since it does not need back light like the liquid crystal display device, more thinned and light-weighed display panel can be achieved, thus luminescent element display panel of active matrix driving type holds an extremely strong position.
Here brief description is given on organic EL element as an example of self luminescent element applied to luminescent element type display.
FIG. 10 is a schematic cross sectional view showing one example of structure of organic EL element.
As shown in FIG. 10, the organic EL element is structured by stacking anode electrode (positive electrode) 112, organic EL layer 113 comprising organic compound (organic material) and the like, and cathode electrode (negative electrode) 114 in this order on one side (upper side in figure) of an insulating substrate 111 such as glass substrate, schematically.
The organic EL layer 113 is structured with, for example, a positive hole transport layer (positive hole injection layer) 113a comprising positive hole transport material (positive hole injection layer forming material), and an electron transporting light emitting layer (light emitting layer) 113b comprising electron transporting light emitting material. Here, as for positive hole transport material and electron transporting light emitting material applied to the organic EL layer 113 (positive hole transport layer 113a and electron transporting light emitting layer 113b), various kinds of organic materials of low molecular and high molecular organic materials are known.
Here, in general, when using low molecular organic material, light emitting efficiency at the organic EL layer is relatively high. However, since deposition method is used in manufacturing process, when forming film only onto the anode electrode within pixel forming region selectively, low molecular material is applied also on a mask surface that is provided to prevent deposition of low molecular material on region other than the afore-mentioned anode electrode. Therefore, there is a problem that material loss during manufacturing is large, and that manufacturing process is not efficient.
On the other hand, when using high molecular organic material, since droplet discharge method (what is called ink jet method) as a wet coating method and the like can be used, liquid droplet can be selectively coated on anode electrode within pixel forming region, thus organic EL layer (positive hole transport layer and electron transporting light emitting layer) can be formed efficiently.
Here, a brief description is given on manufacturing process of organic EL element using high molecular organic material.
FIG. 11 and FIG. 12 are cross sectional view of process flow concerning one example of manufacturing process of display panel (organic EL element) within conventional technique. Here, for convenience of explanation, a case in which only organic EL element is formed on insulating substrate is shown. In addition, the same reference number is used for description concerning the same structure with the afore-mentioned organic EL element described in FIG. 10.
One example of manufacturing process of organic EL element is, first of all as shown in FIG. 11A, to form anode electrode (positive electrode) 112 for each region that is to be formed with each display pixel (pixel forming region) Apx, wherein the pixel forming region Apx is on one side (upper side in figure) of insulating substrate 111 such as glass substrate and the like. Subsequently, as shown in FIG. 11B, barrier wall (bank) 121 comprising insulating material and the like is formed in boundary region of adjacent display pixel. Here, in the pixel forming region Apx surrounded by the barrier wall 121, the afore-mentioned anode electrode 112 is exposed.
Next, as shown in FIG. 11C, by irradiating ultraviolet ray on a surface of the insulating substrate 111 under oxygen gas atmosphere, oxygen radical is generated, organic matter on the surface of the anode electrode 112 is removed by decomposition making the surface of the anode electrode 112 hydrophilic, and radical is also generated on the surface of the barrier wall 121 making the surface of the barrier wall 121 lyophilic.
Next, by irradiating ultraviolet ray under fluoride compound gas atmosphere, to the insulating substrate 111 processed with the aforementioned lyophilic property applying processing, fluorine is bonded on the surface of the barrier wall 121 and made liquid repellent (or water repellent). In contrast, surface of the anode electrode (ITO) keeps 112 lyophilic property.
Next, as shown in FIG. 11D, by using an ink jet device, liquid material (first solution) HMC, which is a positive hole transport material comprising high molecular organic material dispersed or dissolved in solvent, is discharged from ink head IHH in droplet and is coated on the anode electrode 112 having lyophilic property. Subsequently, by conducting drying processing, as shown in FIG. 11E, positive hole transport material is fixed on the anode electrode 112 and thus positive hole transport layer 113a is formed.
Next, in a similar manner, as shown in FIG. 11F, liquid material (second solution) EMC, which is an electron transporting light emitting material comprising high molecular organic material dispersed or dissolved in solvent, is discharged from ink head IHE in droplet and is coated on the positive hole transport layer 113a. Subsequently, by conducting drying processing, as shown in FIG. 12A, electron transporting light emitting material is fixed and thus electron transporting light emitting layer 113b is formed. Here, in coating processing of the liquid material HMC comprising the positive hole transport material and liquid material EMC comprising electron transporting light emitting material, since the surface of the barrier wall 121 has water repellency, even in a case where liquid droplets of liquid materials HMC and EMC land on the barrier wall 121, they are repelled. Thus, liquid materials HMC and EMC are coated only on lyophilic region on the anode electrode 112 within each pixel forming region Apx (that is, organic EL element forming region Ael).
Next, as shown in FIG. 12B, cathode electrode (negative electrode) 114 comprising a shared electrode is formed so as to face the anode electrode 112 by intermediary of the organic EL layer 113 (positive hole transport layer 113a and electron transporting light emitting layer 113b) within each pixel forming region Apx. Subsequently, as shown in FIG. 12C, protective insulating film and sealing resin layer 115 are formed on the insulating substrate 111 including the cathode electrode 114, sealing substrate 116 is attached, and thus organic EL element (organic EL display panel) is obtained.
Such manufacturing method of organic EL element is described in detail in Japanese Patent Application (Laid Open) No. 2003-257656.
Concerning organic EL element having such element structure, as shown in FIG. 10, by applying positive voltage to anode electrode 112 and negative voltage to cathode electrode 114 from direct-current voltage source 115, light hυ (excitation light) is emitted according to energy generated when hole injected into the positive hole transport layer 113a and electron injected into the electron transporting light emitting layer 113b bind again in the organic EL layer 113.
Here, this light hυ can be emitted in arbitrary direction of one side (upper side in figure) or the other side (lower side in figure) of the insulating substrate 111, by forming anode electrode 112 and cathode electrode 114 with electrode materials having transparent or opaque (and light reflecting) properties, respectively. Here, emission intensity of the light hυ is determined according to amount of current that flow between anode electrode 112 and cathode electrode 114.
In the afore-mentioned manufacturing method of display panel (organic EL element), periphery of anode electrode 112 of each display pixel (pixel forming region Apx) is surrounded by barrier wall 121, and after liquid which becomes carrier transport layer material is coated in between the barrier wall 121 as partition, it is dried to form carrier transport layer (for example, the positive hole transport layer 113a and electron transporting light emitting layer 113b). The liquid which becomes carrier transport layer material, that is coated as above, tends to aggregate around periphery of the anode electrode adjacent to the barrier wall due to surface energy. As a result, carrier transport layer in the center of anode electrode becomes relatively thin, and problem arises in that thickness of film becomes uneven. Therefore, approach to form film of carrier transport layer on anode electrode uniformly, by forming film that shows liquid repellency on the surface of barrier wall is made. However, when liquid that becomes carrier transport layer material is dried by heating in the atmosphere, the film that shows liquid repellency degrades, thus it was difficult to make carrier transport layer as uniform film. Here, carrier transport layer is a layer that transport carrier of electron or positive hole when forward bias is applied, and may include light emitting region where electron and positive hole bind again.
Therefore, concerning the afore-mentioned problem, an object of the present invention is to provide display device with carrier transport layer of relatively uniform film thickness, formed in pixel forming region of display pixel, and its manufacturing method.
The present invention, concerning a manufacturing method of a display device provided with a luminescent element that has a carrier transport layer, comprises:
a liquid repellent film forming step to form a liquid repellent film on a surface of a plurality of barrier walls provided on a substrate;
a coating step to coat a carrier transport material containing acidic solution that contains carrier transport layer material on a pixel electrode arranged in between the plurality of barrier walls; and
a drying step to dry the carrier transport material containing acidic solution under inert gas atmosphere.
It is especially effective in a case where the liquid repellent film has a property that liquid repellency degrades under atmosphere containing oxygen.
Preferably, the liquid repellent film comprises triazine thiol compound.
Preferably, at least a surface of the plurality of barrier walls comprises single metal or metal alloy of nonoxide.
Preferably, the plurality of barrier walls are line arrangement that directly or indirectly connect to the luminescent element.
Preferably, the luminescent element is connected to a luminescent driving circuit that has a transistor.
In the present invention, it is preferable that the pixel electrode has a surface comprising metal oxide.
In the present invention, it is preferable that the pixel electrode is applied with lyophilic processing, and the lyophilic processing includes at least one of oxygen plasma processing or UV-ozone processing.
Preferably, at the liquid repellent film forming step, the liquid repellent film is formed selectively on a surface of the plurality of barrier walls.
Preferably, the liquid repellent film is electrically conductive in thickness direction.
In the present invention, a counter electrode forming step to form a counter electrode that electrically connects with the plurality of barrier walls through the liquid repellent film, is provided after the drying step.
The luminescent element may have a structure of top emission type or a bottom emission type.
The present invention is a display device manufactured by the manufacturing method of the display device.
According to the manufacturing method of display device of the present invention, carrier transport layer of relatively uniform film thickness can be formed in pixel forming region of display pixel.